1. In a saucepan, combine the ground ginger and mineral water. Bring to a boil, then reduce heat and simmer for 10 minutes.

2. Remove from heat and strain the ginger mixture through a fine mesh sieve or cheesecloth into a large bowl.

3. Add the sugar (or honey) to the ginger liquid and stir until dissolved.

4. Let the mixture cool to room temperature.

5. Once cooled, stir in the sparkling water and a few drops of lemon juice.

6. Transfer the ginger beer to a clean, airtight container and refrigerate for at least 4 hours, or until chilled.

7. Serve over ice with lemon slices for garnish.